X-ray examination apparatus are known in which the patient is irradiated from different projections by a measuring arrangement consisting of an X-ray source and an X-ray detector and wherein the X-radiation received by the detector is converted into electric signals corresponding to the radiation intensity. In the case of these so-called computer tomographs, these electric signals are conveyed to a computer which calculates therefrom the attenuation coefficients of predetermined points of the examined transverse layer of the patient. These attenuation coefficients can be reproduced on a display apparatus in the form of an image of the examined transverse layer.
In the case of a computer tomography, it is necessary that the dose rate of the x-radiation emitted by the X-ray source be constant to a great degree, since fluctuations of the dose rate would bring about fluctuations of the output signals of the detector without density fluctuations in the patient being present. Thus, such fluctuations would falsify in the measurement result and would produce artifacts in the X-ray image.